San Antonio is a little less than halfway, Houston is a little more.
Oklahoma City is fairly close to halfway between Flint, Michigan and Tucson, Arizona.
Blythe
Seguin, TX
There is 464 miles between Jacksonville, Florida and Chattanooga, Tennessee. The city that is halfway between these two cities would be Macon, Georgia.
Dunn, NC
Walterboro, SC
Florence, SC
Blumpkin City, FL
Oklahoma City, OK
Shamrock, TX
Pensacola, FL
Ocala, Florida is the halfway point between Tampa and Jacksonville. Ocala is the county seat of Marion County, and the 45th most-populate Florida city.